1. Field of the Invention
The present invention relates to a construction machine such as a hydraulic shovel, and more particularly to a frame constitution of a lower traveling body in a construction machine.
2. Description of the Related Art
A conventional hydraulic shovel 100 disclosed in “Crawler-type Vehicle” (Japanese Unexamined Patent Application Publication 2002-178960) comprises a traveling body 101 to enable movement, and a slewing body 102 which is mounted slewably above the traveling body 101, as shown in FIG. 9.
The slewing body 102 comprises a slewing frame 103, and the stewing frame 103 is provided with a body cover 104 accommodating a motor and the like, a cab 105 which defines the operating cabin, a counterweight 106, and so on, for example.
A working device 107 is provided elevatably at the front portion of the slewing body 102.
A truck frame 108 constituting the main body part of the traveling body 101 is constituted by a center frame 109 positioned in the center by means of steel plate welding or the like, and side frames 112 provided on both the left and right sides of the center frame 109 and extending to the front and rear, as shown in FIGS. 10A, 10B, and 10C.
Here, the center frame 109 is constituted by a central circular core 110, and leg parts 111 extending in a front/rear direction and a left/right direction from the outer periphery of the circular core 110 to form an overall H shape.
The leg parts 111 are formed as canning structures by an upper plate portion 111A, a lower plate portion 111B, side plate portions 111C which connect the plate portions 111A, 111B in a vertical direction, and so on.
112, 112 are left and right side frames provided on the tip end side of the leg portions 111 of the center frame 109 by welding. The side frames 112 are formed as frame bodies in a substantially reverse C shape extending in a front/rear direction.
Left and right mudguard covers 125, 125 are disposed respectively on the side frames 112, 112 of the truck frame 108.
The hydraulic shovel 100 described above travels over various types of ground surface by driving crawler belts 117 disposed on the traveling body 101 to rotate. As a result, earth, mud, and so on are churned up by the crawler belts 117.
Here, the mudguard covers 125, 125 provided in the vicinity of the crawler belts 117, 117 are constituted so as to extend in a horizontal direction, and hence the earth, mud, and so on that are churned up by the crawler belts 117 may accumulate on top of the mudguard covers 125, 125.
In this case, a worker must remove the accumulated earth, mud, and so on, and if the earth, mud, and so on are left to accumulate, they cause running resistance when the hydraulic shovel 100 is operated.
To improve earth removal, a constitution has been considered in which the frame of the lower traveling body is divided into a central box-shaped rotary case portion and the pair of truck frame portions, on which the crawler belts are provided, on the two sides of the rotary case portion, whereby the truck frames are connected to the rotary case portion via a pair of leg-shaped connecting members.
According to this constitution, the rotary case portion and the truck frame portions are connected via a pair of connecting members, and hence an open space is formed between the pair of connecting members through which the earth that is churned up by the crawler belt passes and falls to the ground. Thus earth removal can be precipitated favorably.
Incidentally, various loads act on the slewing body 102 of the hydraulic shovel 100, on which the working device 107 is provided, during an operation.
However, the conventional truck frames 108 are constituted by sheet metal, as shown in FIG. 10C, and hence a vertical plate may be provided below the circular core 110 to which the slewing body 102 is connected, and a vertical plate 120 is provided between the upper plate portion 111A and lower plate portion 111B.
Hence stress that is generated by a load transmitted to the circular core 110 which supports the slewing body 102 is transferred smoothly to the vertical plate 120 from the circular core 110, thus eliminating problems relating to strength.
When the truck frame portions and central rotary case portion are constituted separately and joined via connecting members, however, the length of the connecting members is preferably set at no more than a predetermined length from the point of view of problems regarding the strength of the connecting members and the prevention of increases in the moment of loads generated during travel. To shorten the connecting members, a side plate of the rotary case portion to which the connecting members are joined must be formed so as to jut out from the connecting member side.
In this case, the side plate of the rotary case portion is provided at a remove from the location of the upper plate of the rotary case portion on which the slewing body is mounted, and as a result, loads transmitted from the slewing body are transferred to the upper plate having low load-withstanding strength, leading to possible breakage of the rotary case portion depending on the structure thereof.